Vitamin D: What You Need to Know

What is Vitamin D?

As nutrients go, Vitamin D is in a class by itself. That's because vitamin D is actually a hormone that the body produces in response to direct exposure of skin to direct Ultraviolet B (UVB) rays from the sun. Vitamin D is classified as a fat-soluble vitamin, which means that vitamin D you make and what you consume from foods and dietary supplements is stored in fat tissue for later use.

 
 
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Benefits of Vitamin D
Vitamin D enhances your body's absorption of calcium from foods and supplements; it also regulates calcium's movement into, and out of, bones in order to maintain calcium levels in serum in the body. Without enough vitamin D circulating in your blood stream, absorption of adequate calcium is difficult.

That's not all Vitamin D does. Recent science suggests that Vitamin D influences cell growth, immune function, and may help support nervous system functions.

Adequate vitamin D is central to a strong skeleton.

How Much Vitamin D Do You Need?
According to the Institute of Medicine (IOM), the amount of vitamin D recommended daily depends on your age. From age one to 70, get 600 IU daily; people over the age of 70 should get 800 IU of vitamin D each day. Vitamin D requirements do not increase during pregnancy and breastfeeding.

Where Do I Get Vitamin D?
You can get Vitamin D from the sun, limited foods, and supplements.

Strong sunlight triggers vitamin D production in your skin. Your liver, kidneys, and cells throughout the body complete the conversion to vitamin D's most active form, 1,25-vitamin D3.

In theory, you should be able to make all the Vitamin D you need by getting adequate sunlight. In reality, many people do not produce the required vitamin D, and many fail to get what they need from food and dietary supplements. According to the 2010 Dietary Guidelines for Americans, most children and adults consistently come up short for vitamin D.

Several factors affect your vitamin D status. You may not have enough vitamin D in your body if:

  • You cover all exposed skin when outside, or you use sunscreen with an SPF of 8 and above, which effectively blocks most or all of the UVB rays necessary to begin vitamin D production in the skin.
  • You have dark skin, live in areas greater than 20 degrees latitude from the equator, or live in areas with smog and pollution. Darker skin contains melanin, a compound that blocks the production of vitamin D in response to UVB rays.
  • Are overweight. The body stores vitamin D in body fat. Ironically, excessive body fat absorbs and holds onto vitamin D, making it unavailable for supporting bone health and its other important functions. The more body fat, the less available vitamin D is to the body; people with Body Mass Index of ≥ 30 may need more vitamin D than non-obese people to obtain optimal blood levels.
  • You're a senior. As you age, your capacity for producing vitamin D from the sun declines. Older people who stay indoors compound their potential vitamin D deficiency because they limit sunlight exposure.
  • You're a breastfed infant. Human milk is relatively low in vitamin D, and infants who are exclusively breast-fed run a high risk of vitamin D deficiency when they are not also given supplemental vitamin D. The American Academy of Pediatrics recommends that all breast-fed and partially breast-fed infants receive 400 IU of vitamin D daily starting in the first days of life.

Food Sources of Vitamin D
For such an important nutrient, few foods are natural sources of vitamin D. Some commonly-consumed foods, including milk and orange juice, are fortified with vitamin D. Most brands of yogurt and cheese do not contain added vitamin D, however. Here's a list of foods with vitamin D.

Food IUs per serving
Source: Adapted from Dietary Supplement Fact Sheet: Vitamin D.
Salmon (sockeye), cooked, 3 ounces 447
Mackerel, cooked, 3 ounces 388
Tuna, canned in water, drained, 3 ounces 154
Milk, any fat level, vitamin D-fortified, 1 cup 115-124
Orange juice, vitamin D-fortified (check labels for exact amounts) 100
Yougurt, fortified, 6 ounces 80
Egg yolk, 1 large 41

Dietary Supplements
Since relatively few commonly-consumed foods supply vitamin D, it's often difficult to get the vitamin D you need from the diet alone. For example, if you’re between the ages of one to 70, you’d need six eight-ounce glasses of fortified milk or orange juice; about 12 ounces of canned tuna; or a combination of three ounces of mackeral and nearly 18 ounces of fortified yogurt to meet your recommended daily vitamin D intake level. Dietary supplements can fill in gaps in vitamin D consumption, helping you to reach your daily goals.

In addition to inadequate vitamin D in the diet, people who are at particular risk for inadequate vitamin D levels in their blood stream because they avoid direct sunlight, or stay inside, may need a dietary supplement to satisfy their vitamin D requirements. The elderly and overweight may need more vitamin D than the recommended amounts for other adults. Some Experts in the field of vitamin D research believe that higher amounts of vitamin D than those recommended by the Institute of Medicine may be necessary for maintaining higher levels of vitamin D in the blood stream to support bone and general health. To find out how much Vitamin D is right for you, see your doctor and ask them to check your serum levels of 25-hydroxyvitamin D.

Vitamin D supplements have the potential to interact with several common medications and certain medications may impact your body’s Vitamin D status. Ask your doctor about the potential for these interactions.

References

Dietary Supplement Fact Sheet: Vitamin D. http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional

Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.

Heaney RP. Long-latency deficiency disease: insights from calcium and vitamin D. Am J Clin Nutr 2003;78:912-9.

Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr. 2004;79(3):362-371.

Linus Pauling Institute. Micronutrient Information Center – Vitamin B12. Available at: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminD/ Accessed May, 25, 2011.

Nesby-O'Dell S, Scanlon KS, Cogswell ME, et al. Hypovitaminosis D prevalence and determinants among African American and white women of reproductive age: third National Health and Nutrition Examination Survey, 1988-1994. Am J Clin Nutr. 2002;76(1):187-192

Harris SS, Soteriades E, Coolidge JA, Mudgal S, Dawson-Hughes B. Vitamin D insufficiency and hyperparathyroidism in a low income, multiracial, elderly population. J Clin Endocrinol Metab. 2000;85(11):4125-4130. Allain TJ, Dhesi J. Hypovitaminosis D in older adults. Gerontology. 2003;49(5):273-278.

Wagner CL, Greer FR, and the Section on Breastfeeding and Committee on Nutrition. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. American Academy of Pediatrics. 2008;122(5):1142-1152. http://www.aap.org/new/VitaminDreport.pdf

Arunabh S, Pollack S, Yeh J, Aloia JF. Body fat content and 25-hydroxyvitamin D levels in healthy women. J Clin Endocrinol Metab. 2003;88(1):157-161.

Worstsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr 2000;72:690-93.

Bischoff-Ferrari HA, Shao A, Dawson-Hughes B, Hathcock J, Giovannucci E, Willett WC. Benefit-risk assessment of vitamin D supplementation. Osteoporos Int 2010(21):1121-1132.